The move is meant to counter “any provocation coming from North Korea” following Pyongyang’s latest nuclear test on Wednesday, US media quoted the unnamed official as saying on Monday.

Washington and Seoul are already in talks to send further strategic assets to the Korean peninsula, a day after a US B-52 bomber flew over the South in a show of military force.

The United States and South Korea are continuously and closely having discussions on additional deployment of strategic assets,” said Kim Min-seok, a spokesman at the South Korean Defense Ministry, declining to give specifics.

Seoul also said on Monday that it would restrict access to the jointly run Kaesong industrial complex just north of the heavily militarized inter-Korean border to the “minimum necessary level” starting from Tuesday.

North Korea says it exploded a hydrogen bomb last Wednesday, although the United States and other critics doubt this.